This invention relates to electric motors and, more specifically, to motors which are adapted for submersion within a liquid. More particularly, this invention relates to submersible electric motors having means for purging any liquid which leaks into the motor housing.
Motors which are designed for submersion into a liquid generally fall into one of two categories. Some motors, such as those which are to be used in high-pressure environments including deep sea applications, permit environmental liquid to enter the motor since sealing is not feasible under those conditions. The remaining class of submersible motors are, however, sealed since it is generally better to exclude the environmental liquid if possible.
Those skilled in the art will appreciate that environmental liquids are generally corrosive and/or dirty. The prevention of corrosion necessitates the use of relatively exotic and expensive materials; the presence of solid particulate matter increases wear and drag on the moving motor parts, thereby detrimentally affecting the reliability and life of the motor.
Seals substantially reduce, but do not totally eliminate matter on the motor components. Firstly, economic considerations, manufacturing tolerances, and material limitations preclude seals from being absolutely effective.
It is accordingly preferred to employ means in addition to sealing for preventing the contamination of interior motor components by the environmental liquid. Submersible motors generally include a housing. The unoccupied space within the housing can be filled with either a liquid such as oil, or a gas such as air. Liquid is advantageous in that it is relatively incompressible and can accordingly provide some reduction in the differential between the pressures inside and outside the motor housing, thereby reducing the potential for seal failure. The presence of liquid within the housing, however, creates drag losses within the motor which increase as a cubic function of motor speed.
While the forementioned drag losses are substantially reduced by the substitution of gas for liquid in the motor housing, gas is, of course, compressible. Conventionally, submersible motors within gas-filled housings have included an expandable chamber which permits the enclosed gas to expand or contract with the pressure changes associated with changing submersion depth. The volumetric change in gas, however, is concurrent with a temperature change in the gas which must be taken into account in the structural design of the motor.
The present invention provides an air-filled submersible motor comprising a motor, a housing encompassing the motor and including sealing means for substantially preventing the leakage of environmental liquid into the housing, first conduit means for permitting the ingress of gas into the housing and having a first end positioned above the liquid surface, second conduit means for permitting the egress of gas and accumulated liquid out of the housing, and a source of compressed gas coupled to the first end of the first conduit means for supplying gas to the housing interior at a pressure which exceeds the ambient pressure at the level of submersion.
Further details are described in the following Description of the Preferred Embodiment of which the Sole FIGURE is a part.